This application claims the benefit of Korean patent application No. 2000-32247, filed Jun. 12, 2000 in Korea, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display (LCD) device implementing selectable reflective and transmissive modes.
2. Discussion of the Related Art
Generally, a transflective LCD device has advantages of both a transmissive LCD device and a reflective LCD device. Because the transflective LCD device uses a back light as well as an ambient light source, it is not dependent upon exterior light source conditions, and consumes relatively low power.
FIG. 1 is an exploded perspective view illustrating a typical transflective LCD device. The transflective LCD device 11 includes an upper substrate 15 and a lower substrate 21 that are opposed to each other, and a liquid crystal layer 23 interposed therebetween. The upper substrate 15 and the lower substrate 21 are called a color filter substrate and an array substrate, respectively. On the upper substrate 15, a black matrix 16 and a color filter layer 17 including a plurality of red (R), green (G), and blue (B) color filters are formed. The black matrix 16 surrounds each color filter such that an array matrix feature is formed. Further on the upper substrate 15, a common electrode 13 is formed to cover the color filter layer 17 and the black matrix 16.
On the lower substrate 21 opposing the upper substrate 15, a thin film transistor (TFT) xe2x80x9cTxe2x80x9d, as a switching element, is formed in shape of an array matrix corresponding to the color filter layer 17. In addition, a plurality of crossing gate and data lines 25 and 27 are positioned such that each TFT xe2x80x9cTxe2x80x9d is located near each crossing portion of the gate and data lines 25 and 27. The crossing gate and data lines define a pixel region xe2x80x9cPxe2x80x9d. On the pixel region xe2x80x9cPxe2x80x9d, a pixel electrode 19 is formed. The pixel electrode 19 includes a transmissive portion xe2x80x9cAxe2x80x9d and a reflective portion xe2x80x9cCxe2x80x9d.
FIG. 2 is a cross-sectional view illustrating operation modes of the typical transflective LCD device 1. As shown, the transflective LCD device 11 includes the upper substrate 15 having the common electrode 13, the lower substrate 21 having the pixel electrode 19, the liquid crystal layer 23 interposed therebetween, and a back light 41 disposed below the lower substrate 21. The pixel electrode 19 includes a reflective electrode 19b having a through-hole xe2x80x9cAxe2x80x9d and a transparent electrode 19a positioned below the reflective electrode 19b. The transparent electrode 19a is separated from the reflective electrode 19b by a passivation layer 71 interposed therebetween.
For a reflective mode, the transflective LCD device 11 uses a first ray xe2x80x9cBxe2x80x9d of ambient light, which may radiate from an exterior natural light source or from an exterior artificial light source. The first ray xe2x80x9cBxe2x80x9d passes through the upper substrate 15 and is reflected by the reflective electrode 19b back through the liquid crystal layer 23, which is aligned by the application of an electric field between the reflective electrode 19b and the common electrode 13. Accordingly, the aligned liquid crystal layer 23 controls the first ray xe2x80x9cBxe2x80x9d so as to display an image.
For a transmissive mode, the transflective LCD device 11 uses a second ray xe2x80x9cFxe2x80x9d of light, which radiates from the back light 41. The second ray xe2x80x9cFxe2x80x9d sequentially passes through both the transparent 19a and reflective 19b electrodes and the liquid crystal layer 23 which is aligned by the application of an electric field between the transparent electrode 19a and the common electrode 13. Accordingly, the aligned liquid crystal layer 23 controls the second ray xe2x80x9cFxe2x80x9d so as to display an image.
FIG. 3 is an expanded plan view illustrating a portion of an array substrate for a conventional transflective LCD device. As shown in FIG. 3, a gate line 25 is arranged in a transverse direction, and a data line 27, arranged perpendicular to the gate line 25, are both formed upon an array substrate 21 (in FIG. 1). A thin film transistor (TFT) xe2x80x9cTxe2x80x9d is arranged at a position where both the gate line 25 and the data line 27 cross one another. A pixel electrode 19 comprises both a transparent electrode 19a and a reflective electrode 19b is disposed on a pixel region xe2x80x9cPxe2x80x9d defined by the gate line 25 and data line 27. The TFT xe2x80x9cTxe2x80x9d includes a gate electrode 61 to which a scanning signal is applied, a source electrode 63 to which a video signal is applied, and a drain electrode 65 which inputs the video signal to the pixel electrode 19. A gate pad 26 and a source pad 28 are respectively disposed at end portions of the gate line 25 and data line 27. The gate pad 26 and the source pad 28 are to be electrically connected with a drive IC (not shown).
Still referring to FIG. 3, the pixel electrode 19 is a transflective electrode having both the transparent electrode 19a and the reflective electrode 19b. Specifically, the transparent electrode 19a is first formed on the pixel region xe2x80x9cPxe2x80x9d, and is electrically connected with the drain electrode 65 via a first drain contact hole 67. Then, the reflective electrode 19b is formed over the transparent electrode 19a. The reflective electrode 19b is also electrically connected with the drain electrode 65 via the transparent electrode 19a. Thus, the reflective electrode 19b has a through hole xe2x80x9cAxe2x80x9d corresponding to a transmissive portion of the LCD device 11 such that rays of back light 41 (in FIG. 2) can pass through the through hole xe2x80x9cAxe2x80x9d for function in the transmissive mode. Portion xe2x80x9cCxe2x80x9d of the reflective electrode 19b serves as a reflective portion of the LCD device 11 such that rays of the ambient light are thereby reflected.
With reference to FIGS. 4A to 4F, a fabrication process for the array substrate is explained. FIGS. 4A to 4F are sequential cross-sectional views taken along first to third lines xe2x80x9cIIIxe2x80x94IIIxe2x80x9d, xe2x80x9cIVxe2x80x94IVxe2x80x9d, and xe2x80x9cVxe2x80x94Vxe2x80x9d of FIG. 3.
At first, as shown in FIG. 4A, a first metal is deposited and patterned on the transparent array substrate 11 such that a gate pad 26, a gate line 25 (in FIG. 3), and a gate electrode 61 are formed. The gate line extends from the gate pad 26, and the gate electrode 61 protrudes from the gate line 25 (in FIG. 3). Thereafter, a gate-insulating layer 62 and a silicon layer 64 are sequentially formed upon the first metal. The silicon layer 64 comprises an amorphous silicon layer 64a and a doped amorphous silicon layer 64b. 
Next, as shown in FIG. 4B, the silicon layer 64 (in FIG. 4A) is patterned such that an active layer 66a and an ohmic contact layer 66b are formed to have an island-shaped structure positioned above the gate electrode 61. Thereafter, as shown in FIG. 4C, a second metal is deposited over the island-shaped structure and is subsequently patterned such that a source pad 28 (in FIG. 3), a plurality of data lines 27, a source electrode 63, and a drain electrode 65 are formed. The data line 27 crosses the gate line 25 (in FIG. 3) with the source pad 28 (in FIG. 3) being disposed at one end of the data line 27. The source electrode 63 protrudes from the data line 27, and the drain electrode 65 is spaced apart from the source electrode 63.
Thereafter, an exposed portion of the ohmic contact layer 66b is etched away between the source electrode 63 and the drain electrode 65, and a first passivation layer 71 is formed on the overall surface where the source electrode 63 and the drain electrode 65 are formed. The first passivation layer 71 has formed therein a first drain contact hole 67 positioned over the drain electrode 65, a first gate pad contact hole 32 positioned over the gate pad 26, and a first source pad contact hole 37 (in FIG. 3) positioned over the source pad 28 (in FIG. 3).
Next, as shown in FIG. 4D, a transparent conductive material is deposited upon the first passivation layer 71 and subsequently patterned to form a transparent electrode 19a, a first gate pad terminal 35, and a first source pad terminal 39 (in FIG. 3). The transparent electrode 19a electrically contacts the drain electrode 65, via the first drain contact hole 67, and the first gate pad terminal 35 electrically contacts the gate pad 26, via the first gate pad contact hole 32. Additionally, the first source pad terminal 39 (in FIG. 3) electrically contacts the source pad 28 (in FIG. 3) via a first source pad contact hole 37 (in FIG. 3). At this point, the transparent electrode 19a preferably overlaps portions of the data lines 27 formed on both sides of the pixel region (reference xe2x80x9cPxe2x80x9d of FIG. 3).
Next, as shown in FIG. 4E, an inorganic insulating material such as silicon oxide, for example, is deposited upon the transparent electrode 19a and subsequently patterned to form a second passivation layer 77. The second passivation layer 77 comprises a second drain contact hole 79 positioned over the drain electrode 65, a second gate pad contact hole 91 positioned over the gate pad 26, and a second source pad contact hole (not shown) positioned over the source pad 28 (in FIG. 3). The second contact holes 79, 91 expose corresponding portions of the transparent electrode 19a. 
Next, as shown in FIG. 4F, a second metal is deposited upon the second passivation layer and subsequently patterned to form a reflective electrode 19b having a through hole xe2x80x9cAxe2x80x9d, a second gate pad terminal 83, and a second source pad terminal 85 (in FIG. 3). The second metal is preferably aluminum (Al) or aluminum alloy, for example, which have low resistance and high reflectance properties. The reflective electrode 19b electrically contacts the transparent electrode 19a via the second drain contact hole 79 such that the reflective electrode 19b and the drain electrode 65 are electrically interconnected. The second gate pad terminal 83 electrically contacts the first gate pad terminal 35 via the second gate pad contact hole 91 such that the second gate pad terminal 83 and the gate pad 26 are electrically interconnected. The second source pad terminal 85 (in FIG. 3) electrically contacts the first source pad terminal 39 (in FIG. 3) via the second source pad contact hole (not shown) such that the second source pad terminal and the source pad 28 (in FIG. 3) are electrically interconnected.
For the above dual-contact structure, the transparent electrode 19a contacts the drain electrode 65 via the first drain contact hole 67, and the reflective electrode 19b contacts the transparent electrode 19a via the second drain contact hole 79. In other words, the reflective electrode 19b and the transparent electrode 19a electrically contact the drain electrode 65 via the first and second drain contact holes 67 and 79, respectively. Then, all the liquid crystal molecules of the liquid crystal layer (23 in FIG. 2) disposed on the reflective electrode 19b having the through hole xe2x80x9cAxe2x80x9d can be aligned regardless of their individual location. Furthermore, both a first liquid crystal portion disposed on the reflective electrode 19b and a second liquid crystal portion disposed on the through hole xe2x80x9cAxe2x80x9d can both be controlled to have proper alignment direction.
At this point, the transparent electrode 19a is preferably formed of an oxide material such as indium tin oxide (ITO), for example, and the reflective electrode 19b is preferably formed of an aluminum-based metal material, for example, having low resistance and high reflectance properties. However, aluminum-based metals are easily oxidizable. When the oxide material and the aluminum-based metal material make contact with each other, an oxide film is produced on the boundary surface between the oxide and the aluminum-based metal. This oxide film causes a high contact resistance between the drain electrode 65 and the reflective electrode 19b such that operational quality of the TFT (xe2x80x9cTxe2x80x9d in FIG. 3) deteriorates. Furthermore, use of these materials results in poor adhesion at the gate pad 26 and the source pad 28 (in FIG. 3), as explained hereinafter.
The drive IC (not shown) is installed on an LCD device by applying various methods. A tape carrier package (TCP) is an example of the various installing methods. Using the TCP method, the drive IC is not installed directly on the array substrate, but is included as an independent package. Then, the independent drive IC package is attached to each pad of the LCD device such that signals are applied from the drive IC to each pad. As shown in FIG. 4F, the aluminum-based metal that forms the reflective electrode 19b, the second gate pad terminal 83, and the second source pad terminal 85 (in FIG. 3), is conventionally used for an uppermost layer of each pad. Because the aluminum-based metal is highly ductile and easily oxidizable, adhesion between the TCP and the uppermost layer easily deteriorates when an exterior force is acted thereon.
If an error occurs on attaching the TCP to the array substrate, the TCP is usually removed from the array substrate for the purpose of rework. In this case, the aluminum-based electrodes where the TCP is attached are easily deformed since the aluminum-based metal is highly ductile.
The reflective electrode, the second gate pad terminal, and the second source pad terminal, all of which are made from the aluminum-based metal, may be exposed to degenerative conditions due to misalignment errors between the TCP and the pad. Accordingly, any or all of the reflective electrode, the second gate pad terminal and the second source pad terminal can be easily corroded due to effects resulting from various cleaning processes used to assemble the device, thereby causing defects in the LCD device.
Accordingly, the present invention is directed to a transflective LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a transflective LCD device having a low contact resistance between a drain electrode and a pixel electrode with transparent and reflective electrodes such that a TFT has an improved operation quality.
Another object of the present invention is to provide a transflective LCD device having a good adhesion between a pad and a TCP.
Another object of the present invention is to provide a liquid crystal display device including: a substrate; at least one gate line and at least one gate electrode formed on the transparent substrate; a gate insulating layer formed over the at least one gate line and the at least one gate electrode; a silicon layer formed on the gate insulating layer, the silicon layer being positioned above the at least one gate electrode; a source electrode and a drain electrode formed on the silicon layer and spaced apart from each other with the silicon layer overlapped therebetween, wherein the at least one gate electrode, the source electrode, the drain electrode, and the silicon layer comprise a thin film transistor (TFT); at least one data line; a first passivation layer covering the at least one data line; a reflective electrode covering a portion of a pixel region defined by the at least one gate line and the at least one data line; a second passivation layer formed on the reflective electrode; and a transparent electrode formed on the second passivation layer, wherein the transparent electrode is disposed in the pixel region.
In another aspect, a transflective liquid crystal display device includes a substrate, a gate pad and a gate line formed on the substrate, the gate line including a gate electrode that extends from the gate pad in one direction, the gate pad being disposed on one side of the substrate, a gate-insulating layer formed on the substrate, the gate-insulating layer covering the gate line and the gate electrode, a silicon layer formed on the gate-insulating layer, the silicon layer being disposed over the gate electrode, a source electrode and a drain electrode spaced apart from each other with the silicon layer centered therebetween, a data line formed on the gate-insulating layer, the data line crossing the gate line, connecting with the source electrode, and having a source pad at one end thereof, a pixel region defined by the crossing gate line and the data line, a first passivation layer formed on the source electrode, a reflective electrode formed on the first passivation layer, the reflective electrode having a through hole and being disposed in the pixel region, a second passivation layer formed on the reflective electrode, wherein the second passivation layer includes a drain contact hole positioned over the drain electrode, a gate pad contact hole positioned over the gate pad, and a source pad contact hole positioned over the source pad, each contact hole passing through the second passivation layer, a transparent electrode formed over the reflective electrode; a gate pad terminal formed over the gate pad, and a source pad terminal formed over the source pad, wherein the transparent electrode contacts the drain electrode via the drain contact hole, the gate pad terminal contacts the gate pad via the gate pad contact hole, and the source pad terminal contacts the source pad via the source pad contact hole.
In another aspect, a method of fabricating a transflective liquid crystal display device includes the steps of forming a gate pad, a gate line, and a gate electrode on a substrate, the gate pad being disposed on one side of the substrate, the gate line extending from the gate pad in one direction, forming a gate-insulating layer on the substrate, the gate insulating layer covering the gate line and the gate electrode, forming a silicon layer on the gate-insulating layer, the silicon layer having an island shape and being disposed over the gate electrode, forming a source pad, a data line, a source electrode, and a drain electrode on the gate insulating layer, wherein the data line crosses the gate line and extends from the source pad, and the source electrode and the drain electrode are spaced apart from each other and overlap a portion of the silicon layer, forming a first passivation layer on the substrate to cover the source and drain electrodes, forming a reflective electrode on the first passivation layer, the reflective electrode having a hole therethrough, forming a second passivation layer on the reflective electrode, forming a drain contact hole, a gate pad contact hole, and a source pad contact hole pass through the second passivation layer positioned over the drain electrode, the gate pad, and the source pad, respectively, and forming a transparent electrode on the second passivation layer, the transparent electrode contacting the drain electrode via the drain contact hole, contacting the gate pad via the gate pad contact hole, and contacting the source pad via the source pad contact hole.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.